1. Field of the Invention
This invention relates to an image processing method and apparatus. More particularly, the invention relates to an image processing method and apparatus for reading a color original, for example, and expressing differences in color by a black-and-white output in conformity with the particular color.
2. Description of the Prior Art
A conventional method of expressing a difference in color by a difference in a pattern is described in the specification of Japanese Patent Publication No. 63-59303. According to this disclosure, colors in an original document are identified, patterns corresponding to the identified colors are selected from a memory storing a plurality of patterns, and the patterns are output in a single color. As a result, chromatic portions contained in the image of the original are reproduced in the form of corresponding patterns and all other portions are output in the form of luminance information.
In the example of the prior art described above, however, when the luminance distribution of the entire document is sampled in the usual manner also when AE (automatic exposure) is applied, even areas (chromatic portions) of the document at which luminance information is not output are sampled. As a consequence, AE cannot be performed accurately.
Further, in a case where a document has a background or base color, it is desired that this background-color portion not be converted into a pattern. In the prior art, however, the background-color is replaced by a pattern and printed when it is judged that the background of the document is chromatic.